Stegosauridae

Stegosauridae Temporal range: Middle Jurassic - Early Cretaceous, 170–100Ma PreЄ Є O S D C P T J K Pg N
Life restoration of Stegosaurus stenops
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Order:	†Ornithischia
Suborder:	†Stegosauria
Superfamily:	†Stegosauroidea
Family:	†Stegosauridae Marsh, 1880
Type species
†Stegosaurus stenops Marsh, 1877

Stegosauridae is a family of thyreophoran dinosaurs comprising all stegosaurs more closely related to Stegosaurus than to Huayangosaurus.^[1] Their fossil range's extent into the late Early Cretaceous exceeds that of other stegosaurs, such as huayangosaurids, which had died out by the end of the Late Jurassic. They are characterized by rows of osteoderms along the top of their neck, trunk and tail which graded with varying abruptness from the anterior plates to the caudal spines at a point posterior to the dorsal vertebrae.^[2] These may have had a number of functions: display and/or thermoregulation for the broad flat osteoderms, defense for the spikes.^[3][4][5]

Paleobiology

Comparison among three well-known stegosaurids

General anatomy

Stegosaurids were usually large and powerful dinosaurs. Their front legs were shorter than their rear making them slow-moving dinosaurs. When Othniel Charles Marsh first found Stegosaurus, he portrayed the genus with very short front legs and neck. But new evidence shows that they had relatively long body parts.^[6] Several species show sexual dimorphism in the sacrum with the putative female having an extra pair of sacral ribs. There are also two sizes of parascapular spines in Lexovisaurus which can be ascribed to such variation.^[3][7]

Bite

In 2010 Míriam Reichel, using the 3D-modelling software ZBrush, created two digital models of Stegosaurus teeth differing in the presence or not of serrations. She proved that Stegosaurus had rhamphotheca. She also found that stegosaurs were capable of shearing small branches, and suggested that the same data could be applied to other stegosaurids.^[8]

Evolution

In contrast with early stegosaurs, like Huayangosaurus, stegosaurid skulls are shallower and the difference between the long hindlimb and short forelimb larger.^[2] The osteoderms of stegosaurids can attain a large size either as the broad plates of Stegosaurus or the long spikes of Kentrosaurus.^[6]

Classification

Taxonomy

Stegosauridae is usually divided into two main subfamilies: Dacentrurinae and Stegosaurinae.^[9] Stegosaurinae are usually characterized by large sizes. The earliest stegosaur is thought to be Lexovisaurus^[10] from the Bathonian of England. There was found a massive femur of the juvenile Lexovisaurus.

This is a list of stegosaurian genera by classification and location:

Suborder Thyreophora

Infraorder Stegosauria

• Family Stegosauridae
  • Lexovisaurus (=Loricatosaurus)^[11] — (United Kingdom & France)
  • Kentrosaurus — (Tanzania, Africa)
  • Paranthodon — (South Africa)
  • Monkonosaurus — (Tibet, China)
    • Tuojiangosaurus — (Sichuan, China)
    • Subfamily Dacentrurinae^[9]
      • Dacentrurus — (United Kingdom, France & Spain)^[12]
      • Miragaia — (Portugal)^[13]
    • Subfamily Stegosaurinae
      • Stegosaurus — (Wyoming, USA)
      • Hesperosaurus — (Wyoming, USA)
      • Wuerhosaurus — (Xinjiang, Western China)

Basal Stegosaurids

Like basal stegosaurs, stegosaurids of such a persuasion, like Lexovisaurus, Kentrosaurus or Tuojiangosaurus, are characterized by the comparatively large osteoderms running along their backs and reduced lateral osteoderms. Contrasting with the abrupt transition from plate to spike in stegosaurines, primitive stegosaurids have their plates grade into spines in a zone with osteoderms showing an intermediate shape.^[2][14]

Dacentrurinae

Proposed by Mateus et al. (2009) to include Dacentrurus and all stegosaurs closer in relation to it than to Stegosaurus. Currently, only one other member of Dacentrurinae is known: Miragaia.^[13][15] They usually have long back spines and necks.

Stegosaurinae

First recognized by Nopcsa in 1915, it comprises according to the definition of Sereno (1998) the eponymous Stegosaurus and all stegosaurs more closely related with it than to Dacentrurus. Besides the type, it includes Hesperosaurus and Wuerhosaurus.^[1]

Phylogeny

A cladogram by paleontologist Kenneth Carpenter.^[16]

Carpenter's proposal states that Wuerhosaurus and Hesperosaurus are more closely related to Tuojiangosaurus and Dacentrurus than to Stegosaurus. However, Thomas Holtz has proposed that Hypsirophus, Stegosaurus, Hesperosaurus and Wuerhosaurus form a subfamily-Stegosaurinae:^[9]

Timeline of genera

References